Road transportation is responsible for 17% of worldwide emissions of carbon dioxide, according to the report of the International Energy Agency, 2011a. Passenger light-duty vehicles account for 60% of that amount. The number of these vehicles is assumed to double between 2010 and 2035 due to their fast growing number in emerging countries, according to the report of the Intentional Energy Agency, 2011b. Reducing the CO2 emissions of passenger light-duty vehicles is thus a major task toward achieving the long-term goal of reducing total carbon dioxide emissions. Using compressed natural gas (CNG) instead of gasoline or diesel is one attractive option to reduce the CO2 emissions of passenger and light-duty vehicles. CNG mainly consists of methane which has a higher hydrogen to carbon (H to C) ratio compared to gasoline or diesel. This higher H to C ratio of methane leads to a reduction of CO2 emissions in the order of 20-25%, for the same engine-efficiency, according to Semin, R. (2008), “A technical review of compressed natural gas as an alternative fuel for internal combustion engines” Am. J. Engg. & Applied Sci, 1(4), 302-311. Among all possible gas engines, the dual fuel engine is one of the most promising. In the dual fuel engine, the gas is injected into the intake manifold. The premixed air-gas mixture is then ignited with a small amount of directly injected diesel. This engine has the potential of achieving diesel-like efficiencies without the need for a lean de-NOX system, according to Serrano and Bertrand, 2012, “Exploring the potential of dual fuel diesel-CNG combustion for passenger car engine”, in IFAC 2012.
Combustion in the gas/diesel dual fuel engine has been extensively investigated. It has been found, that even if the ratio of diesel fuel to total fuel mass is very small, the influence of the diesel injection on the whole combustion is large. More specifically, the sensitivity of combustion phasing and combustion noise on start of injection is high. (Serrano and Bertrand). The start of combustion depends on the start of injection of the diesel and on the ignition delay of the diesel. The latter is mainly dependant on the chemical reaction kinetics of the diesel fuel. This process is very sensitive to small changes in pressure, temperature or cylinder charge composition.
Combustion processes which are prone to external disturbances can best be controlled by using feedback control based on the measured cylinder pressure. Feedback control based on the measured cylinder pressure has been applied successfully to conventional diesel engines, as disclosed in WO 2009/143 858 A1. It has also been applied to the control of HCCI engines, as by Olsson, J., Tunestal, P., Johansson, B., et al. (2001) in “Closed-loop control of an hcci engine” SAE TRANSACTIONS, 110(3), 1076-1085, as an example. And it has also been applied to many other combustion types.